1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device and, more particularly, to a method of fabricating metal lines in a semiconductor integrated circuit.
2. Description of the Related Art
An integrated semiconductor device comprises transistors, resistances and capacitors, and requires metal lines for fabricating the device on a silicon wafer. Because the metal lines transmit electrical signals, characteristics such as low electrical resistance, low cost, and high reliability, are required in the metal lines. Aluminum is one of the materials satisfying the above-described requirements. Accordingly, aluminum is widely used in making the metal line.
As the degree of integration of an integrated semiconductor device is increased, however, the width and the thickness of metal lines as well as the size of contact holes decrease. As the size of contact holes decrease, its aspect ratio is increased, and hence it becomes more difficult to fill the contact hole with aluminum. Accordingly, the technology of filling the contact holes completely with aluminum becomes more critical as the degree and level of integration in semiconductor devices increase.
One of the technologies used for completely filling high aspect ratio contact holes with aluminum is a chemical vapor deposition aluminum (CVD-Al) process. Generally, there are two types of CVD-Al process. A first type is a blanket aluminum process, and a second type is a selective aluminum process.
The blanket aluminum process utilizes and takes advantage of the excellent step coverage characteristic of aluminum metal. The blanket Al process deposits aluminum metal over the entire surface of a wafer to fill up contact holes. As is generally known, however, the CVD-Al process exhibits a peculiar growth characteristic beyond a certain thickness by generating a greater wafer roughness and by not completely filling small contact holes. On the other hand, the selective aluminum process utilizes the property of a difference in growth rate of Al on an insulation layer and a conductive layer in a restricted area such as via contacts and, hence, can not be employed in forming a metal contact involving a barrier metal. Accordingly, a new technology for lowering the contact resistance and a metal line resistance, and for completely filling up contact holes is necessary and essential for fabricating current day highly integrated semiconductor devices.
Japanese patent publication No. 4-171940 discloses a fabrication process for filling up contact holes of a semiconductor device. According to the fabrication process disclosed and taught by this publication, an ohmic contact layer is initially deposited and then a barrier layer is deposited as an intermediate layer in a contact hole. Subsequently, either an Al layer or an Al alloy layer is deposited on the intermediate layer. After removing most of the Al layer on the sidewall of the contact hole and most of the barrier layer at the bottom of the contact hole, the remaining Al layer is re-flowed to the bottom of the contact hole. Finally, a new Al layer is deposited in the contact hole to fill up the contact hole.
U.S. Pat. No. 6,022,800 discloses another fabrication process for filling up a contact hole. According to the fabrication process disclosed and taught in this patent, a first titanium nitride TiN layer is deposited over the entire surface of the contact hole by a chemical vapor deposition (CVD) method, and thereafter a second TiN layer is deposited on the first TiN layer by a physical vapor deposition (PVD) method. Thereafter, a sufficient amount of tungsten is deposited to fill up the contact hole.
Japanese patent publication No. 10-64902 discloses another fabrication process for filling up a contact hole. According to the fabrication process disclosed and taught by this publication, a barrier layer in the form of a Ti layer or a TiN layer is initially deposited on a wafer surface by a physical vapor deposition PVD method. A metal layer with improved wettability, comprising aluminum and titanium, is then deposited on the barrier layer to prevent a metal line from reacting with a sub-silicon or with a sub-metal line. Aluminum is then re-flowed to fill up the contact hole.
Another approach that has been used in filling up contact holes is called a preferential metal deposition (PMD) process. The PMD process deposits an aluminum layer in the same way as the blanket Al process does and by improving the selectivity ratio of an aluminum sub-layer.
Referring to FIG. 1A, in the PMD process, an insulation layer 3 is initially deposited on a silicon substrate 1. After generating a contact hole 35, a barrier metal layer 5 is deposited on the contact hole 35 and the insulation layer 3. An anti-nucleation layer (ANL) 7 is generated on the surface of the barrier metal layer 5, except in the contact hole 35. A physical vapor deposition (PVD) process, or a chemical vapor deposition (CVD) process performed in the condition of worse conformability, deposits an oxidation metal such as aluminum Al, zirconium Zr, titanium Ti, strontium Sr, magnesium Mg, barium Ba, calcium Ca, cerium Ce, and yttrium Y, etc. Subsequently, either the PVD process or the CVD process oxidizes the deposited metal layer by exposure to air or by oxygen plasma process to generate the ANL 7. Referring to FIG. 1b to FIG. 1d, a CVD-Al process selectively deposits the metal layer 9 in the contact hole 35. Subsequently, a physical vapor deposition aluminum PVD-Al process deposits an aluminum layer 11 and fills up the contact hole 35 by a re-flow process.
However, the re-flowed PVD-Al according to the above-described patents and to the PMD-Al process is migrated on the ANL, and the migration is very active because the deposited Al does not react with the ANL. As a result, uncontrolled grain growth can be observed in the deposited Al, which generates greater depth difference of the grain boundary. As a result, fabrication defects, such as ring defects, can occur during the succeeding process steps.
To overcome the above described problems, preferred embodiments of the present invention provide a method of fabricating a semiconductor device that inhibits atomic migration of aluminum deposited by a PVD method and abnormal growth of the aluminum grain, by which abnormal metal line patterns in a semiconductor integrated circuit is avoided.
The preferred embodiments of the present invention provide a method of fabricating a semiconductor device having a recess region in an insulation layer on a silicon substrate, comprising the steps of depositing a barrier metal over the entire surface of the insulation layer including the substrate surface in the recess region, depositing selectively an anti-nucleation layer on the barrier metal except in the recess region, depositing a CVD-Al layer on the barrier metal in the recess region, depositing a metal or a metal alloy for inhibiting aluminum migration on the barrier metal except in the recess region, and depositing a PVD-Al layer and re-flowing the PVD-Al layer.
The metal or the metal alloy inhibiting aluminum migration may be selected from Ti, TiN, Ti/TiN, Ta, TaN and Ta/TaN with a thickness of less than 10 nm.
These and other features of the present invention will be readily apparent to those of ordinary skill in the art upon review of the detailed description that follows.